1. Field of the Invention
The present invention relates to a fabricating method for capacitor of a semiconductor device.
2. Description of the Related Art
The conventional method of building a capacitor into a semiconductor device has involved forming a dielectric film in the shape of a tantalum oxide, barium-strontium titanate or other oxide film on to a bottom electrode of polysilicon, metal or oxide conductive layer, then forming a top electrode of ruthenium, iridium or a similar substance.
When fabricating capacitors of this sort it is common to implement heat-treatment within oxygen, activated oxygen or ozone after formation of the dielectric film. This serves to increase dielectric constant by crystallizing the dielectric film, and to reduce current leakage by compensating oxygen deficit (cf. Japanese Laid-Open Publication No.82915/97).
FIG. 16 is cross-section illustrating an example of the configuration of a conventional semiconductor device.
As FIG. 16 shows, a device isolating silicon oxide film 1602 and a diffusion layer 1603 forming part of a MOS transistor or a similar device are formed on the surface of a silicon wafer 1601, followed by an interlayer insulator 1604. Then, after a contact hole 1605 has been formed in the film 1604, a bottom electrode 1606 is formed in the shape of an interlayer wiring film 1606a and conductive layer 1606b in polysilicon or a similar substance. Next, a tantalum oxide or other dielectric film 1607 is formed over the whole surface, and the capacitor is heat-treated in oxygen, activated oxygen or ozone as mentioned above. Finally, it is completed with the formation of a top electrode 1608 having a film of ruthenium, iridium or a similar substance which covers all the film 1607.
However, conventional capacitors such as those illustrated in FIG. 16 suffer from the following defects.
As has been stated above, it has been common conventional practice to subject the capacitor to heat-treatment in an atmosphere of oxygen or the like after formation of the film 1607. As a result it sometimes happens that a silicon oxide layer 1606c is formed in the vicinity of the interfacial boundary between the films 1606a and 1606b. This leads to the formation, in addition to the above mentioned capacitor, of another capacitor comprising the conductive films 1606a and 1606b along with the insulation layer 1606c, so that two serially connected capacitors exist within the semiconductor device. Consequently, the total dielectric constant of the capacitors formed in such a semiconductor device falls below the intended level.
Moreover, it sometimes happens that during heat-treatment the layer 1606b oxidizes, thereby tending to increase the unevenness of the surface and resultant current leakage.
Conversely, the oxygen within the film 1607 may be released during heat-treatment, leading to oxygen deficit and consequent increased current leakage.
If the conductive layer 1606b is formed of a different material such as a metal or a conductive oxide, it may happen that a barrier layer (not shown in the drawing) forms between the films 1606b and 1606c. In such cases, heat-treatment causes this barrier layer to oxidize into a dielectric layer, so that there is a risk of a capacitor being formed between the layers 1606b and 1606a. The result again is that the total dielectric constant of the capacitors falls below the intended level.
Such defects combine to lower the yield of the semiconductor device, and result in increased costs.